This invention relates to a circuit arrangement for operating a high-pressure discharge lamp which supplies a luminous flux of at least 60% of the nominal luminous flux within 1 s after ignition. The circuit arrangement comprises
a static converter for generating a DC voltage, PA1 a commutator provided with lamp connection terminals, PA1 means A for current stabilization during stable lamp operation by controlling the static converter, and PA1 means B for operating the lamp with an increased run-up current and an increased power as compared with nominal or normal rated lamp operation and on the basis of an instantaneous lamp voltage signal.
A circuit arrangement of the kind mentioned in the opening paragraph is known, inter alia, from EP-A-443795.
Important types of high-pressure discharge lamps are high-pressure sodium lamps, high-pressure mercury lamps and metal halide lamps. A comparatively high luminous flux immediately after switching-on of the lamp is required, especially when a high-pressure discharge lamp serves as a motorcar headlamp. Metal halide lamps whose discharge vessels contain, inter alia, Xe are particularly suitable for motorcar headlamp applications.
A disadvantage of the known arrangement is that the luminous flux of the lamp after ignition in the case of a cold start exhibits a considerable fluctuation during the run-up of the lamp to a stable operating condition. This fluctuation may amount to more than half of the nominal rated luminous flux under certain circumstances. The occurrence of such a major luminous flux fluctuation is unpleasant both for the user and for the other road users, and may even lead to hazardous traffic situations.
The nominal or rated lamp voltage often lies between 60 V and 110 V in practice. This depends to a high degree on the lamp manufacturing technology.
A reduction of the nominal rated lamp voltage, all other circumstances remaining the same, will lead to an increase in the nominal current, which results in a rise in ohmic losses.
The choice of a higher lamp voltage, all other circumstances remaining the same, in general leads to a greater electrode spacing. This is undesirable particularly for reflector lamps, as in the case of motorcar headlamp systems, because the formation of the illumination beam depends to a high degree on the dimension of the light source, i.e. the discharge path between the electrodes of the discharge lamp.